Heretofore, in a method of producing the silver halide photographic emulsion, silver halide grains are formed by reacting an aqueous silver salt solution and an aqueous halogen salt solution in a reacting vessel, and then, from among excessive halogenated substances which remained in the system, unnecessary substances such as potassium ions, sodium ions, nitric acid ions and ammonia are removed by means of washing so that the silver halide photographic emulsion is obtained.
When the density of salts in the reacting vessel is high, the adsorption property, or affinity to the surface of the silver halide grains, is hindered due to the existence of the above-mentioned unnecessary substances as well as that dissolution of the silver halide grains and unevenness of grain size and composition accompanying thereto occurs so that mono-dispersed grains cannot be obtained. Therefore, the efficiency of spectral sensitizing dyes, sensitizers and stabilizers is extremely diminished. In addition, when the density of salts is high, drying property and storage stability of the light-sensitive material is reduced, requiring that the salts be removed.
Incidentally, in the above-mentioned production method, in a method which adds the aqueous halogen salt solution, there was a shortcoming that localization ions occur in the vicinity of an aqueous solution pouring port and, resulting in non-uniformity in the grain size or composition of the silver halide grains produced.
As a method which solves the above-mentioned non-uniformity of grains, recently, Japanese Patent Publication Open to Public Inspection (hereinafter, referred to as Japanese Patent O.P.I. Publication) Nos. 183417/1989 and 183654/1989 and WO Nos. 89/0683 and 89/06831 disclose technologies which do not supply silver salt and halogen salt in the form of an aqueous solution but supply it in the form of fine silver halide grains.
However, even in the case of the above-mentioned fine grains supplying method, unnecessary substances, described as above, remain in the system after the formation of the grains. Therefore, it is desirable to desalt and remove them.
Japanese Patent O.P.I. Publication Nos. 172816/1990 and 172817/1990 disclose technologies about the desairing method of the silver halide fine-grain emulsion. Aforesaid technologies are respectively one which desalt a fine grain silver halide emulsion while adding it to the reacting vessel and one which desalts the fine grain silver halide emulsion during adding to the emulsion in the reacting vessel. However, due to technologies described in the above-mentioned patents, aging fluctuation of grains occur in the mixing vessel, provided separately from the reacting vessel, because aforesaid fine grain emulsion is not desalted. Therefore, aforesaid fine grain emulsion solution could not be effectively stored so that it was necessary to precisely control the production schedule. Specifically, since Japanese Patent O.P.I. Publication No. 172817/1990 desalts a solution after a solution supplied it from the mixing vessel and a solution taken up from the reacting vessel or desalts the solution picked up from the reacting vessel, the desalting effect was not sufficient and remains of unnecessary ions were observed. Therefore, this technology does not employ a suitable desalting method.